1. Field of the Invention
The present invention relates to organic electronic components, and more particularly to issues due to the localizing of an active organic layer on forming of electronic components or the like. The invention more specifically relates to a method of structuring an active organic layer deposited on a substrate, and to the step of chemically etching the active layer, on manufacturing of an organic diode.
2. Description of Related Art
In the field of microelectronics, that is, of micrometric-scale electronic components, the electronic components have been initially developed from inorganic materials such as silicon or gallium arsenide (GaAs), particularly to form the active layer of the components, the latter being formed of a stack of such inorganic layers.
Such inorganic electronic components have the disadvantage of being expensive to manufacture and of being rigid, and accordingly of being fragile and impossible to use for certain applications.
Thus, the active layers of electronic components are now more and more frequently made of organic materials, such as polymers, for example, which have the advantage of being easy to manufacture at a large scale, of having a good mechanical and/or thermal behavior, of having a flexible structure and of being easy to recycle. Further, polymers being soluble in a solvent, the latter may advantageously be deposited in a layer by low-cost and easy-to-implement deposition methods such as, particularly, spin coating, inkjet deposition, or silk-screening deposition.
This is why displays based on OLED or Organic Light-Emitting Diodes or based on OTFT or Organic Thin-Film Transistors can now currently be encountered. Such electronic components are usually formed of a stack of organic and/or inorganic layers where the active layer is made of an organic material.
However, such a stack of organic and/or inorganic layers raises a number of issues, particularly on forming of organic diodes, which requires a highly-homogeneous deposition of an organic active layer, the stacking of the layers of an organic diode usually being as follows: a substrate made of glass, plastic, silicon, etc., a local conductive layer made of indium-tin oxide or ITO, metal, a conductive polymer, etc., a injector layer made of poly(3,4-ethylenedioxythiophene) poly(styrenesulfonate) or PEDOT:PSS, for example, an active layer made of a mixture of n- and p-type semiconductor called bulk heterojunction, and a local conductive layer made of metal or a conductive polymer, for example.
Indeed, in the manufacturing of an organic diode, the deposition of the active organic layer is the critical step. Such an organic layer should be very homogeneous and with no defect capable of causing an electric leakage between the two conductive layers of the diode. The active organic layer is usually deposited by a spin coating method, which provides film-forming deposits. However, spin coating does not enable to structure the active organic layer. To structure the active layer, after its deposition on the substrate, several techniques are used, including subtractive etching, also called direct etching, and lift-off.
Subtractive etching, for example illustrated in FIG. 1, comprises, after having deposited an active layer 1 on a substrate 2 at a step 1a, depositing during a step 1b a polymer 3, and this locally on active layer 1 by any appropriate means such as inkjet or silk-screening, for example, the polymer 3 for example being a fluoropolymer sold under trade name CYTOP®. At a step 1c, the portions of active layer 1 which are not covered with the polymer are then chemically etched by application of a solvent such as xylene, chlorobenzene, tetraline, toluene, etc., after which the polymer is stripped, that is, dissolved with a solvent which does not etch active layer 1, such as perfluorotributylamine (FC43) for example.
Such a subtractive etching is particularly described in document WO 2011/004198.
Subtractive etching has the disadvantage of deteriorating the active layer, as can be seen in FIG. 2, which is an optical microscope view of the surface of the active layer after a subtractive etching. Indeed, the chemical action of the etch solvent causes an overetching of the active layer on the pattern edges.
The second structuring technique, called lift-off, comprises, referring to FIG. 3, depositing a sacrificial resist layer 4 on a substrate 2 at a step 1a, and then structuring the sacrificial layer 4 to create a pattern 5 in the sacrificial layer 4 by chemical etching, for example, at a step 1b. At step 1c, an active organic layer 1 is deposited on sacrificial layer 4 and at the bottom of pattern 5, after which, at a last step 1d, sacrificial layer 4 is dissolved in a solvent bath, generally acetone, to only leave the pattern of active layer 1 on substrate 2.
This type of “lift-off” structuring method is especially described in documents US 2005/0048414 and US 2011/0012097.
The lift-off technique also has the disadvantage of deteriorating active layer 1. Indeed, active layer 1 is damaged by the action of the acetone bath during the dissolution of the sacrificial layer, the acetone bath lasting for approximately 20 minutes. Such an acetone bath weakens active layer 1, resulting in poorly-defined pattern edges and pittings, as can be seen in FIG. 4A and respectively 4B.